Field of the Invention
Embodiments of the present invention generally relate to a device, such as a cell phone, with a feedback system that compensates for the capacitance change that occurs when a cell phone is held in the hand or adjacent the head of a user.
Description of the Related Art
Cellular phones, such as mobile phones, have many desirable features that make everyday life easier. For instance, mobile phones can receive emails, text messages and other data for the end user to utilize. Additionally, the mobile phone can send emails, text messages and other data from the mobile phone. The mobile phone typically operates on a wireless network provided by any one of the various cell phone carriers. The data sent to and from the mobile phones require the mobile phone to operate at an increasing number of frequencies to support all of the components and antennas of the mobile phone.
3G and 4G cellular phone systems require diversity of multiple-input multiple-output (MIMO) antennas. So there are at least two antennas operating at the same frequency at the same time. In mobile data platforms, like smart phones, tablets, portable personal hotspots, and notebook computers there is not enough room to physically separate the antennas. In these small platforms, the antenna systems suffer from efficiency degradation due to mutual coupling between the antennas. In the past, efficiency degradation has been dealt with by de-tuning the secondary antenna to decouple the secondary antenna from the primary antenna. Decoupling the secondary antenna is effective with a fixed primary and secondary antenna but is becoming a problem in modern devices where the primary and secondary antennas can be swapped. In addition, for MIMO systems, optimum performance may occur when there is greater balance between the two antennas.
The MIMO antenna systems can further suffer when the phone is held in the hand or placed near the ear for talking, as the head and hand can affect the device performance by interfering with the antennas. In fact, upon release of one mobile phone where antenna interference was a well documented problem, it was remarked that “You're holding it wrong” in regards to the mobile phone. In other words, simply by holding the phone, the antenna system performance worsened. This occurrence is sometimes referred to as the head to hand effect. The antenna system performance problem has continued to this day.
Having the ability to “tune” and “de-tune” the two antennas to fit the changing RF environment will again enhance overall system performance.